Detersive systems have been used for many years in many cleaning environments including laundry, warewashing, hard surface cleaning, and other applications. Typically, detersive systems are concentrates comprising mixtures of cleaning ingredients that when mixed with water form a cleaning medium or use composition. Service water, containing some concentration of hardness ions, supplied by local water utilities is most commonly used in making the use composition. Hardness ions are typically undesirable in conjunction with detersive systems since they interfere in the soil removal mechanism. The quality of service water varies from place to place throughout the country and can vary in the amount of hardness and can vary in the type of hardness components. Hardness typically comprises metal ions including calcium, magnesium, iron, manganese, and other typically divalent or trivalent metal cations, depending on the source of the water. The presence of hardness cations in service water can substantially reduce the detersive action or effectiveness of a detersive system, can result in the incomplete cleaning of laundry, dishware, hard surfaces, and other soiled items or surfaces and can leave films or scale comprising the hardness cation and/or components of the detersive system.
A great deal of attention in recent years has been given to the components of detersive systems that reduce the effects of the hardness components. Common hardness sequestering agents comprise inorganic chemicals such as a condensed phosphate compound and a zeolite, and organic sequestrants such as EDTA, organic phosphonates and organic phosphinates. Such agents are effective in treating hardness in service water by a chemical reaction which keeps the ions in the aqueous bulk detersive system but reduces the hardness effect of the ions on the detersive systems. These agents can be effective but can result in both economic and ecological disadvantages.
Recently, liquid membrane softening agents have been prepared for hardness treating or water softening. Such liquid agents can be used in detersive systems at low concentration and can effectively soften service water through a mechanism of removing hardness ions from aqueous media used in detersive systems with little adverse environmental impact, or compatibility problems in detersive systems. Such systems work through an organic phase, containing a complexing agent, dispersed in the bulk aqueous phase or aqueous detersive system. The organic phase contains an internal dispersed aqueous phase. Hardness ions in the bulk aqueous phase are transferred to the internal aqueous phase through the organic phase by the complexing agent. We believe that the driving force of the softening effect is caused by the chemical potential difference between the inner aqueous phase and the bulk aqueous solution. The phase stability and efficacy of the softening agent is, in part, in direct proportion to the characteristics of the complexing agent.
We have discovered a novel complexing agent that improves the stability and softening properties of the liquid membrane agent. The softening agent of the invention displays unexpectedly superior stability properties and hardness ion transfer properties. Prior art complexing agents tend to leach from the organic phase into the bulk aqueous phase during use thereby diminishing the effectiveness of the liquid membrane softening agents. The softening agent of the present invention is designed to be virtually water insoluble in high pH environments, resulting in no leaching of the complexing agent from the organic phase into the bulk detersive aqueous phase.